Bladder for an infusion assembly

ABSTRACT

Bladders and elastomeric pumps for infusion assemblies are provided. For example, a bladder may comprise a body extending over a length from a first end to an opposing second end; an outer diameter; an inner diameter; and a wall thickness. The wall thickness may gradually transition from a first wall thickness at the first end to a second wall thickness at the second end. In other embodiments, the wall thickness at a midpoint of the length is different than the wall thickness at each of the first end and the second end. An elastomeric pump may comprise an inflatable elastomeric bladder and a mandrel. The bladder includes a body extending over a bladder length from a first bladder end to an opposing second bladder end and a wall thickness, which is different at a midpoint of the bladder length than at each of the first and second bladder ends.

RELATED APPLICATION

The present application is the national stage entry of InternationalPatent Application No. PCT/US2017/018586 having a filing date of Feb.20, 2017, which is incorporated herein by reference in its entirety.

FIELD

The present invention relates to liquid dispensing apparatus andpertains particularly to bladders for elastomeric infusion assemblies.

BACKGROUND

Often, patients are intravenously supplied with pharmaceutically activeliquids at a controlled rate over a long period of time. Preferably,such infusion is accomplished while the patient is in an ambulatorystate. A few devices have been developed in the past for accomplishingthis purpose.

Typically, an infusion assembly includes an inflatable elastomericbladder forming a liquid container that is supported by a mandrel, aswell as a flow control valve or device and tubing for supply of theliquid to the patient. The walls of the bladder are forced to expandwhen filled with the liquid and provide the pressure for expelling theliquid. Usually, conventional infusion assemblies are filled by hand bymeans of a syringe, which often requires an inordinate amount of force.Another drawback to the prior art assemblies is that such assembliesprovide pressures and flow rates that can vary widely with the volume ofliquid therein. Therefore, conventional assemblies do not have areasonably stable pressure and flow rate over the infusion period. Inaddition, conventional bladders frequently have difficulty dispensingsubstantially all of the liquid by the end of the infusion period, andit is undesirable to have liquid remaining in the bladder.

Accordingly, infusion assemblies that overcome one or more drawbacks ofknown infusion assemblies would be desirable. In particular, infusionassemblies having mandrel and/or bladder configurations that improveconsistency in the pressure and flow rate provided by the assembly wouldbe beneficial. For example, modifying the mandrel outer diameter toreduce the crack and/or fill pressure and/or to decrease the residualvolume of liquid at the end of an infusion period would be advantageous.As another example, modifying a wall thickness of the bladder such thatthe wall thickness is non-uniform to reduce crack and/or fill pressureand/or to provide more consistent infusion pressure and flow rate wouldbe helpful.

SUMMARY

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one aspect, the present subject matter is directed to an elastomericbladder for an elastomeric pump. The bladder comprises a body extendingover a length from a first end to an opposing second end; an outerdiameter; an inner diameter; and a wall thickness. The wall thicknessgradually transitions from a first wall thickness at the first end to asecond wall thickness at the second end.

It should be appreciated that the bladder may be further configured withany of the additional features as described herein. For instance, insome embodiments, the wall thickness at the first end is greater thanthe wall thickness at the second end. In other embodiments, the wallthickness at the second end is greater than the wall thickness at thefirst end. The outer diameter of the bladder may be constant over thelength. Further, the inner diameter may gradually transition from afirst inner diameter at the first end to a second inner diameter at thesecond end.

In another aspect, the present subject matter is directed to anelastomeric bladder for an elastomeric pump. The bladder comprises abody extending over a length from a first end to an opposing second end;an outer diameter; an inner diameter; and a wall thickness. The wallthickness at a midpoint of the length is different than the wallthickness at each of the first end and the second end.

It should be appreciated that the bladder may be further configured withany of the additional features as described herein. For example, in someembodiments, the wall thickness at the midpoint of the length is lessthan the wall thickness at each of the first end and the second end suchthat the wall thickness tapers from each of the first end and the secondend toward the midpoint. The outer diameter may be constant over thelength. Further, in some embodiments, the inner diameter increases fromeach of the first end and the second end toward the midpoint. Moreover,each of the first end and the second end may define a groove about anouter perimeter of the bladder for receipt of an O-ring.

In yet another aspect, the present subject matter is directed to anelastomeric pump for an infusion assembly. The elastomeric pumpcomprises an inflatable elastomeric bladder and a mandrel. The bladderincludes a body extending over a bladder length from a first bladder endto an opposing second bladder end, a bladder outer diameter, a bladderinner diameter, and a wall thickness. The bladder is disposed on themandrel and is sealingly secured on the mandrel near each of the firstbladder end and the second bladder end. Further, the wall thickness at amidpoint of the bladder length is different than the wall thickness ateach of the first bladder end and the second bladder end.

It should be appreciated that the elastomeric pump may be furtherconfigured with any of the additional features as described herein. Asan example, in some embodiments, the wall thickness at the first bladderend is greater than the wall thickness at the second bladder end. Inother embodiments, the wall thickness at the second bladder end isgreater than the wall thickness at the first bladder end. In still otherembodiments, the wall thickness at the midpoint of the bladder length isless than the wall thickness at each of the first bladder end and thesecond bladder end such that the wall thickness tapers from each of thefirst bladder end and the second bladder end toward the midpoint of thebladder length. Moreover, each of the first bladder end and the secondbladder end may define a groove about an outer perimeter of the bladderfor receipt of an O-ring that secures the bladder to the mandrel.

Additionally, the mandrel may include a mandrel body extending over amandrel length from a first mandrel end to an opposing second mandrelend, as well as a mandrel outer diameter. In some embodiments, themandrel outer diameter at a midpoint of the mandrel length is greaterthan the mandrel outer diameter at each of the first mandrel end and thesecond mandrel end such that the mandrel is a generally convex mandrel.In some instances of such embodiments, the wall thickness of the bladderat the midpoint of the bladder length may be less than the wallthickness at each of the first bladder end and the second bladder endsuch that the wall thickness tapers from each of the first bladder endand the second bladder end toward the midpoint of the bladder length.

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 is a side view of an infusion assembly having a protectivehousing or shell according to an exemplary embodiment of the presentsubject matter.

FIG. 2 is a side view of the infusion assembly of FIG. 1, with theprotective housing or shell omitted.

FIG. 3 is a perspective view of a mandrel of an infusion assemblyaccording to an exemplary embodiment of the present subject matter.

FIG. 4 is a cross-section view of the mandrel of FIG. 3.

FIG. 5 is a perspective view of a mandrel of an infusion assemblyaccording to an exemplary embodiment of the present subject matter.

FIG. 6 is a cross-section view of the mandrel of FIG. 5.

FIG. 7 is a perspective view of a mandrel of an infusion assemblyaccording to an exemplary embodiment of the present subject matter.

FIG. 8 is a perspective view of a mandrel of an infusion assemblyaccording to an exemplary embodiment of the present subject matter.

FIG. 9 is a perspective view of a bladder of an infusion assemblyaccording to an exemplary embodiment of the present subject matter.

FIG. 10 is a cross-section view of the bladder of FIG. 9.

FIG. 11 is a perspective view of a bladder of an infusion assemblyaccording to an exemplary embodiment of the present subject matter.

FIG. 12 is an end view of the bladder of FIG. 11.

FIG. 13 is a cross-section view of the bladder of FIG. 11 according toan exemplary embodiment of the present subject matter.

FIG. 14 is a cross-section view of the bladder of FIG. 11 according toanother exemplary embodiment of the present subject matter.

FIG. 15 provides a graph of crack and fill pressures for a bladderformed according to an exemplary embodiment of the present subjectmatter and disposed on a mandrel having a known configuration.

FIG. 16 provides a graph of the flow rate for a bladder formed accordingto an exemplary embodiment of the present subject matter and disposed ona mandrel having a known configuration.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Moreover, the particular naming of the components, capitalization ofterms, the attributes, data structures, or any other programming orstructural aspect is not mandatory or significant, and the mechanismsthat implement the invention or its features may have different names,formats, or protocols. Also, the particular division of functionalitybetween the various components described herein is merely exemplary andnot mandatory; functions performed by a single component may instead beperformed by multiple components, and functions performed by multiplecomponents may instead performed by a single component.

Further, the detailed description uses numerical and letter designationsto refer to features in the drawings. Like or similar designations inthe drawings and description have been used to refer to like or similarparts of the invention. As used herein, the terms “first,” “second,” and“third” may be used interchangeably to distinguish one component fromanother and are not intended to signify location or importance of theindividual components.

Referring to the drawings, FIGS. 1 and 2 illustrate an exemplaryembodiment of an elastomeric pump for an infusion assembly in accordancewith the present subject matter. The elastomeric infusion pump 10 ofinfusion assembly 11 comprises an outer collapsible substantiallynon-stretchable housing or shell 12, protectively mounted over areservoir 14 and a support member 16. More particularly, the collapsiblehousing 12 has a substantially spherical configuration for confining andguiding an inflatable reservoir or bladder 14 into a concentric positionaround a central support member or mandrel 16, enabling the bladder 14to expand naturally in a spherical configuration as will be described.The collapsible housing 12 has coaxial openings defined by tubularsleeve extensions 18, 20 through which ends of the mandrel 16 extend.The collapsible housing 12 may be, e.g., a non-stretch blow moldedhousing of from five to ten mils in thickness and made of a materialsuch as polyurethane, PVC film, and/or polyethylene that is transparent.This forms a simple, inexpensive, compact unit with a certain amount ofprotection for the elastic reservoir. Certain applications may require atougher collapsible housing 12. In such cases, the housing 12 should betransparent, UV stable, flexible, and highly resistant to puncturing,e.g., the housing 12 may be constructed of a material such as toughcomposites in a flexible form such as a fabric such as the materialavailable under the trademark Kevlar.

The bladder 14, which is an inflatable reservoir, is mounted on themandrel 16, e.g., using a press fit or a clearance fit. The bladder 14may be a single sleeve or multiple sleeves, e.g., the bladder 14 maycomprise an inner sleeve that is a chemically inert sleeve and an outersleeve or sleeves that are highly elastic. The bladder 14 will bedescribed in greater detail below.

The central support member or mandrel 16 has a first end 22 and a secondend 24, and the mandrel 16 includes circular grooves 26 (FIGS. 3, 4) ateach end 22, 24 thereof into which portions of the sleeve 14 and housing12 are biased by means of a pair of O-rings 28. More particularly, anO-ring 28 secures the bladder 14 to the mandrel 16 at each of the firstand second ends 22, 24 of the mandrel 16. Each O-ring 28 fits into thegroove 26 at the respective mandrel end 22, 24 such that the bladder 14is secured between the O-ring 28 and the groove 26 at each mandrel end22, 24. Further, the first end 22 includes a first cup-shaped cap 30,and the second end 24 includes a second cup-shaped cap 32. First andsecond caps 30, 32 extend over and protectively cover the O-ringconnections for clamping the bladder 14 and housing 12 to the mandrel16. In exemplary embodiments, the caps 30, 32 are releasably coupled tothe ends 22, 24. The infusion assembly 11 further includes a tubing set,having a tube 34 having a filter (not shown) and a connector (not shown)at a distal tube end, that extends from the second end 24 of the mandrel16 to provide a means for connecting and dispensing a fluid to a site,such as a vein of a patient.

It will be appreciated that the bladder 14 expands and contracts toreceive and dispense a fluid. Pressure acts on the fluid as it isinjected into the bladder 14 to expand the bladder from an initialunexpanded state to a maximum expanded state. The maximum expanded stateaccommodates a fill volume. Typically, the fluid is injected from asyringe-type device and passes through a one-way valve connector beforeit enters the bladder, and the pressures upstream of the one-way valveconnector generally are greater than the pressures within the bladder.As such, the upstream pressures move the liquid through the valveconnector, then through one end of the mandrel 16, through a port in themandrel, and against an inner surface 36 of the bladder 14. The crackpressure indicates the force that must be transmitted by the fluid toovercome the initial resistance to expansion of the inflatable bladder14. The fill pressure indicates the forces required for gradualexpansion of the bladder 14 between its ends attached to the mandrel 16;the expansion is generally in a radial direction with respect to acentral axis A of the pump 10. The fill pressures initially decreasefrom the maximum crack pressure and then increase to a maximum when thefill volume is achieved.

Referring now to FIGS. 3 and 4, a perspective view and a cross-sectionview are provided of a mandrel 16 according to an exemplary embodimentof the present subject matter. As shown in the depicted embodiment, themandrel 16 has a body 38 extending over a length L_(M) between the firstend 22 and the opposing second end 24. More particularly, the body 38extends from a first body end 38 a to a second body end 38 b, where thebody ends 38 a, 38 b are just axially inward from the O-ring grooves 26defined in mandrel 16. Further, the mandrel 16 has an inlet port 40 onone end 22, 24; the inlet port 40 is defined at the first end 22 in theillustrated embodiment. A fill port 42 is defined in the body 38 betweenthe first end 22 and the second end 24; in the depicted embodiment, thefill port 42 is defined near the first end 22. In addition, a first bore44 extends within the body 38 and is in fluid communication with theinlet port 40 and fill port 42. More particularly, the first bore 44extends coaxially with the central axis A of the elastomeric pump 10from the first end 22 to the fill port 42, which extends transverselythrough the mandrel body 38. Fluid enters the elastomeric pump 10through the mandrel inlet port 40 and flows through the fill port 42into the reservoir formed by the bladder 14. To dispense the fluid fromthe reservoir, the fluid enters a dispense port 43 and flows through asecond coaxial bore 46 to an outlet port 48 defined at or near thesecond end 24; the outlet port 48 is in fluid communication with thetube 34, which delivers the fluid to a patient. It will be appreciatedthat one or more check valves may be included in the infusion pumpassembly, e.g., to prevent fluid from flowing from the reservoir backthrough the inlet port 40 or from prematurely flowing from the reservoirto the tube 34 for delivery to the patient.

The body 38 of mandrel 16 has an outer diameter D_(M) that variesbetween the first end 22, a midpoint of the length M_(M), and the secondend 24. For instance, in the embodiment shown in FIGS. 3 and 4, themandrel 16 has a first outer diameter D_(M1) at the first body end 38 athat is smaller or less than a midpoint outer diameter D_(MM). Themidpoint outer diameter D_(MM) is smaller or less than a second outerdiameter D_(M2) at the second body end 38 b. As such, the midpoint outerdiameter D_(MM) is different than the outer diameter at each of thefirst and second body ends 38 a, 38 b, and the mandrel 16 is generallytapered between the first and second ends 22, 24, e.g., mandrel 16 istapered from the second body end 38 b to the first body end 38 a. Thatis, in the exemplary embodiment depicted in FIGS. 3 and 4, the outerdiameter D_(M) gradually increases from the first body end 38 a to thesecond body end 38 b or gradually decreases or tapers from the secondbody end 38 b to the first body end 38 a, such that the outer diameterD_(M) is slightly smaller at each point along the mandrel body lengthL_(M) from the second body end 38 b to the first body end 38 a. Bytapering the outer diameter D_(M) of mandrel 16 in the region of thefill port 42, which is defined near the first body end 38 a in thedepicted embodiment, the crack and fill pressure may be reduced due to adecrease in resistance the fluid must overcome to initiate filling thereservoir defined by the bladder 14. For example, the tapered mandrel 16allows pre-stretching of the elastomeric bladder 14 across the workingarea of the elastomer, i.e., the pre-stretch may be tapered to match theway the balloon inflates and deflates. Further, the tapered mandrel 16may encourage the reservoir to fill more evenly because the elastomericreservoir elongation will begin near one end of the mandrel 16 and movetoward the opposite end.

In other embodiments, the outer diameter D_(M) may gradually decreasefrom the first body end 38 a to the second body end 38 b, such that themandrel body 38 is tapered from the first body end 38 a to the secondbody end 38 b. Stated differently, the outer diameter D_(M) maygradually increase from the second body end 38 b to the first body end38 a. More specifically, the first outer diameter D_(M1) at the firstbody end 38 a may be greater or larger than the midpoint outer diameterD_(MM), and in turn, the midpoint outer diameter D_(MM) may be greateror larger than the second outer diameter D_(M2) at the second body end38 b. As such, the midpoint outer diameter D_(MM) is different than theouter diameter at each of the first and second body ends 38 a, 38 b, butunlike the embodiment depicted in FIGS. 3 and 4, the mandrel 16 isgenerally tapered from the first body end 38 a to the second body end 38b. Accordingly, in such embodiments, the outer diameter D_(M) graduallydecreases from the first body end 38 a to the second body end 38 b suchthat the outer diameter D_(M) is slightly smaller at each point alongthe mandrel body length L_(M) from the first body end 38 a to the secondbody end 38 b.

Turning to FIGS. 5 and 6, a perspective view and a cross-section vieware provided of a mandrel 16 according to another exemplary embodimentof the present subject matter. As shown in the depicted embodiment, themidpoint outer diameter D_(MM) is less than the outer diameter at eachof the first body end 38 a and the second body end 38 b such that themandrel 16 is a generally concave mandrel. That is, the midpoint outerdiameter D_(MM) is smaller or less than both the first outer diameterD_(M1) and the second outer diameter D_(M2) such that the outer diameterD_(M) tapers from each body end 38 a, 38 b toward the midpoint M_(M) andis smaller in the middle of the mandrel body 38 than at either body end38 a, 38 b. Further, the fill port 42 is defined generally at themidpoint M_(M) of the mandrel body length L_(M), where the mandreldiameter D_(M) is the smallest.

FIG. 7 provides a perspective view of a mandrel 16 according to anotherexemplary embodiment of the present subject matter. Similar to theembodiment depicted in FIGS. 5 and 6, the mandrel 16 shown in FIG. 7 hasa reduced outer diameter D_(M) around the midpoint M_(M) of the mandrellength L_(M). However, unlike the embodiment of FIGS. 5 and 6, themandrel depicted in FIG. 7 does not have a smoothly tapered outerdiameter D_(M). Rather, the outer diameter is stepped from the firstdiameter D_(M1) to the midpoint diameter D_(MM) and from the midpointdiameter D_(MM) to the second diameter D_(M2); in some embodiments, thefirst and second diameters D_(M1), D_(M2) may be substantially equal.Thus, as illustrated in FIG. 7, the outer diameter D_(M) does notgradually or smoothly transition from one diameter to another butabruptly changes from one diameter to another.

Reducing outer diameter D_(M) of the mandrel 16 around the port 42defined in the mandrel body 38 defines a gap between an outer surface 50of the mandrel 16 and the inner surface 36 of the bladder 14 around theport 42. The gap at the fill port 42 may reduce the crack and fillpressure of the elastomeric pump 10, as well as provide more uniformfilling of the reservoir around the mandrel 16. Further, when the fillport 42 is defined at approximately the mandrel midpoint MM, such thatthe gap is approximately centered with respect to mandrel body 38, theelastomeric pump 10 may experience more uniform, centered filling of thebladder reservoir.

In other embodiments, such as the embodiment of mandrel 16 illustratedin the perspective view of FIG. 8, the outer diameter D_(M) may beincreased or larger in the region of the midpoint M_(M) compared to thefirst body end 38 a and the second body end 38 b, such that the mandrel16 is a generally convex mandrel. That is, the midpoint outer diameterD_(MM) is greater or larger than both the first outer diameter D_(M1)and the second outer diameter D_(M2) such that the outer diameter D_(M)tapers from approximately the midpoint M_(M) toward the body ends 38 a,38 b and is smaller at the ends of the mandrel body 38 than in themidsection. The outer diameter D_(M) may be substantially the same ateach body end 38 a, 38 b and may gradually and smoothly transition fromthe largest diameter at or near the midpoint M_(M) to the smallerdiameters at each body end 38 a, 38 b. Further, the fill port 42 may bedefined generally at the midpoint M_(M) of the mandrel body lengthL_(M), where the mandrel diameter D_(M) is the largest.

By increasing the mandrel outer diameter D_(M) in the midsection of thelength L_(M), the bladder 14 may be pre-stretched in a manner thattapers the pre-stretch across the working area of the elastomericbladder in a way that matches the inflation and deflation of thebladder. As such, the pre-stretch mirrors the elastomer elongation,which is greatest in the midsection of the bladder 14 and tapers offtoward the O-ring seals at the ends of the reservoir. Accordingly, theuniformity of the incremental pressure and/or flow rate may beincreased. Moreover, the volume of fluid retained in the reservoir atthe end of the infusion period may be reduced. More particularly, theincreased mandrel outer diameter D_(M) is the same location where theelastomeric bladder 14 stretches the most and, thus, has the greatestlikelihood to retain fluid. By increasing the mandrel outer diameterD_(M), part of the volume for retained fluid is instead occupied by themandrel 16, thereby reducing the overall volume of fluid retained in thereservoir.

Referring now to FIGS. 9 and 10, a perspective view and a cross-sectionview are provided of a bladder 14 according to an exemplary embodimentof the present subject matter. Referring particularly to FIG. 9, thebladder 14 has a first end 52 and a second end 54; when assembled with amandrel 16, the bladder first end 52 is positioned adjacent the mandrelfirst end 22 and the bladder second end 54 is positioned adjacent themandrel second end 24. A body 56 of the bladder extends between theopposing bladder ends 52, 54, and the body 56 has a length L_(B). Thebladder body 56 has a generally constant outer diameter D_(B) over thelength L_(B). As further illustrated in FIG. 9, each bladder end 52, 54defines a groove 58 about its outer perimeter for receipt of an O-ring(not shown).

As most shown in the cross-section view of FIG. 10, the bladder 14 has awall thickness t and an inner diameter dB that each vary along thelength L_(B). More particularly, the bladder 14 has a first innerdiameter d_(B1) at the first end 52 that is smaller or less than amidpoint inner diameter d_(BM). The midpoint inner diameter d_(BM) isgreater or larger than a second inner diameter d_(B2) at the second end54. As such, the midpoint inner diameter d_(BM) is different than theinner diameter at each of the first and second ends 52, 54, although thefirst inner diameter d_(B1) may be substantially equal to the secondinner diameter d_(B2). Because the bladder outer diameter DB remainssubstantially constant along the length L_(B), the varying bladder innerdiameter dB indicates the wall thickness t of the bladder 14 variesalong the length L_(B). More specifically, the bladder wall thickness tis generally tapered from the midpoint M_(B) to each of the first end 52and second end 54, i.e., the bladder 14 has a midpoint wall thicknesst_(M) at the midpoint M_(B), a first wall thickness t₁ at the first end52, and a second wall thickness t₂ at the second end 54. The innerdiameter d_(B) gradually decreases or tapers from the midpoint M_(B) tothe ends 52, 54, such that the inner diameter d_(B) is slightly smallerat each point along the bladder body length L_(B) from the midpointM_(B) to the first end 52 and from the midpoint M_(B) to the second end54. Stated differently, the wall thickness t is tapered toward themidpoint M_(B), i.e., the wall thickness t decreases from each end 52,54 toward the midpoint M_(B). Further, the wall thickness t is greatest,i.e., the bladder 14 is thickest at each end 52, 54. The thickness ofbladder 14 at ends 52, 54 helps ensure there is adequate bladdermaterial at the ends 52, 54 to define grooves 58.

A decreased bladder wall thickness tin the bladder midsection helps topromote uniform filling of the reservoir formed by the bladder 14 whenthe fill port 42 is aligned with the thinner bladder midsection, e.g.,by creating a path of least resistance at the midsection, where there isless material force to overcome to initiate filling because of thedecreased wall thickness t. Uniform filling may aid in providing a moreconsistent pressure and flow rate as the reservoir empties during theinfusion.

FIGS. 11 and 12 provide a perspective view and an end view of a bladder14 according to another exemplary embodiment of the present subjectmatter. As shown in the depicted embodiment, a plurality of ribs 60 maybe defined along an outer surface 62 of the bladder 14. The ribs 60 maybe evenly spaced apart from one another about a circumference of thebladder or may have any other suitable configuration. The ribs 60 may beformed from the material from which the bladder 14 is made such that theribs 60 and bladder 14 are one integral component.

FIGS. 13 and 14 provide cross-section views of the bladder 14 of FIGS.11 and 12 according to two exemplary embodiments of the present subjectmatter. Turning first to FIG. 13, the bladder 14 of FIGS. 11 and 12 mayhave a wall thickness t and inner diameter dB that each vary similarlyto the bladder 14 depicted in FIGS. 9 and 10. That is, the bladder 14illustrated in FIG. 13 has a first inner diameter d_(B1) at the bladderfirst end 52 that is smaller or less than a midpoint inner diameterd_(BM). The midpoint inner diameter d_(BM) is greater or larger than asecond inner diameter d_(B2) at the second end 54. As such, the midpointinner diameter d_(BM) is different than the inner diameter at each ofthe first and second ends 52, 54, although the first inner diameterd_(B1) may be substantially equal to the second inner diameter d_(B2).Further, the wall thickness t of the bladder 14 varies along the lengthL_(B). More specifically, the bladder wall thickness t is generallytapered from the midpoint M_(B) to each of the first end 52 and secondend 54, i.e., the bladder 14 has a midpoint wall thickness t_(M) at themidpoint M_(B), a first wall thickness t₁ at the first end 52, and asecond wall thickness t₂ at the second end 54. The inner diameter dBgradually decreases or tapers from the midpoint MB to the ends 52, 54,such that the inner diameter d_(B) is slightly smaller at each pointalong the bladder body length L_(B) from the midpoint M_(B) to the firstend 52 and from the midpoint M_(B) to the second end 54. Stateddifferently, the wall thickness t is tapered toward the midpoint M_(B),i.e., the wall thickness t decreases from each end 52, 54 toward themidpoint M_(B). As such, the wall thickness t is greatest, i.e., thebladder 14 is thickest at each end 52, 54. Tapering the bladder wallthickness tin the midsection as shown in FIGS. 9, 10, and 13 may haveseveral benefits, as described in greater detail above.

As illustrated in FIG. 14, in other embodiments, the bladder wallthickness t may be tapered from one end of the bladder 14 to the other.More particularly, the bladder 14 has a first inner diameter d_(B1) atthe first end 52 that is greater or larger than a midpoint innerdiameter d_(BM). The midpoint inner diameter d_(BM) is greater or largerthan a second inner diameter d_(B2) at the second end 54. As such, themidpoint inner diameter d_(BM) is different than the inner diameter ateach of the first and second ends 52, 54, and the bladder inner diameteris generally tapered from the first end 52 to the second end 54. In theexemplary embodiment depicted in FIG. 14, the inner diameter d_(B)gradually decreases or tapers from the first end 52 to the second end54, such that the inner diameter d_(B) is slightly smaller at each pointalong the bladder body length L_(B) from the first end 52 to the secondend 54.

Further, the bladder wall thickness t is different at each point fromthe first end 52 to the second end 54, and more specifically, the wallthickness t increases from the first end 52 to the second end 54. Asshown in FIG. 14, the wall thickness t gradually and smoothly increasesfrom the first end 52 to the second 54. Described differently, the wallthickness t is tapered from the second end 54 to the first end 52, i.e.,the wall thickness t gradually decreases from the second end 54 ofbladder 14 to the first end 52 of bladder 14. Accordingly, the bladder14 is thinnest at the first end 52, where the wall thickness t is thesmallest or least, and thickest at the second end 54, where the wallthickness t is the largest or greatest.

By tapering the wall thickness t as shown in FIG. 14 and aligning thefill port 42 with the thinnest part of the bladder 14, the reservoirformed by the bladder 14 may more uniformly fill with fluid. Aspreviously described, the thinnest bladder wall section provides a pathof least resistance because, compared to sections where the bladder isthicker, there is less material force to overcome to initiate filling.As such, the crack pressure of the pump 10 may be lowered. Further,uniform filling also may help provide a more consistence pressure andflow rate as the reservoir empties during an infusion procedure.

In some embodiments, the bladder 14 may be made from a silicone or apolyisoprene material. For instance, an appropriate silicone orpolyisoprene material may be one that forms inflatable tubes; results ina maximum pressure, as measured a short distance downstream of the firstport, within a desired range when inflated with a predetermined volumeof liquid; and provides sufficient constricting forces to expelsubstantially all the liquid. Of course, other materials also may besuitable for forming bladder 14. Further, an exemplary range of wallthicknesses t for bladder 14 is from about 0.075 inches up to about0.180 inches. An exemplary range of the inner diameters d_(B) of bladder14 is from approximately 0.355 inches to approximately 0.600 inches.Various combinations of bladder length L_(B), wall thickness t, innerdiameter d_(B), and suitable materials may yield bladders having fillvolumes in the range of about 50 to about 600 ml of liquid.

Moreover, suitable combinations of the mandrels 16 and bladders 14described herein may be used to optimize the performance of elastomericinfusion pump 10. For example, a bladder 14 described in the aboveexemplary embodiments may be secured to a mandrel 16 described in theabove exemplary embodiments. In other embodiments, an exemplary bladder14 described above may be secured to a known mandrel, or a known bladdermay be secured to an exemplary mandrel 16 described above, to form anelastomeric infusion pump 10. The bladder and mandrel combination may beselected to minimize crack pressure, have less variability in the flowprofile of the infusion pump 10, and/or have a higher flow rateaccuracy. Other advantages also may be realized by using one or more ofthe configurations described herein.

FIG. 15 provides a graph of crack and fill pressures and FIG. 16provides a graph of the flow rate for an exemplary bladder 14 disposedon a mandrel having a known configuration. More specifically, FIGS. 15and 16 provide graphs of data for a bladder 14 made from a siliconeelastomer KEG 2000-20 and configured as shown and described with respectto FIG. 13. For the data sets illustrated in FIGS. 15 and 16, thebladder 14 has a fill volume of 100 ml and an infusion rate of 5ml/hour.

As shown in FIG. 15, the exemplary bladder 14 has a maximum crackpressure and a maximum fill pressure for each cycle, and the maximumcrack and fill pressures are below 20 psig. FIG. 16 depicts that theflow rate of fluid from the bladder 14 eventually decays toapproximately zero (0) grams/hour as the bladder 14 empties, but theflow rate remains substantially steady, gradually transitioning from afirst flow rate to a second flow rate, which are within about one (1)gram/hour of one another, as the fluid is dispensed from the bladder 14.Accordingly, FIGS. 15 and 16 provide an example that bladders 14 made asdescribed herein may have lower crack and fill pressures and moreuniform flow rates compared to known bladders and elastomeric pumpconfigurations.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. An elastomeric bladder for an elastomeric pump,comprising: an expandable body extending longitudinally between opposingfirst and second connecting end portions, where at least portion of anouter diameter of each of the first and second connecting end portionsis less than an outer diameter of the body, the body extendinglongitudinally over a length from a first end adjacent the firstconnecting end portion of the bladder to an opposing second end adjacentthe second connecting end portion of the bladder, the body furtherincluding an outer diameter, an inner diameter, and a wall thicknessdefined between the inner and outer diameter, wherein the wall thicknessgradually decreases from a first wall thickness at the first end to asecond, smaller, wall thickness at the second end, wherein an innerdiameter of the body gradually increases from a first inner diameter atthe first end to a second, larger, inner diameter at the second end,wherein the body only expands in the radial direction.
 2. The bladder ofclaim 1, further comprising a plurality of ribs projecting from andlongitudinally along an outer surface of the bladder along a length ofthe body.
 3. The bladder of claim 1, wherein an outer surface of thebladder includes a first decreasing tapered segment between the body andthe first connecting end portion and a second decreasing tapered segmentbetween the body and the second connecting end portion.
 4. The bladderof claim 1, wherein the outer diameter of the body is constant over thelength of the body.
 5. The bladder of claim 1, wherein an inner diameterat the first connecting end portion and an inner diameter at the secondconnecting end portion varies from an inner diameter of the body,wherein the body is configured to receive a fluid at the second endbecause the wall thickness at the second end is less than the wallthickness at the first end such that there is less material force toovercome to initiate filing because of the decreased wall thickness. 6.An elastomeric bladder for an elastomeric pump, comprising: anexpandable body extending longitudinally between opposing first andsecond connecting end portions, where at least portion of an outerdiameter of each of the first and second connecting end portions is lessthan an outer diameter of the body, the body extending longitudinallyover a length from a first end adjacent the first connecting end portionof the bladder to an opposing second end adjacent the second connectingend portion of the bladder, the body further including an outerdiameter, an inner diameter, and a wall thickness defined between theinner and outer diameter, wherein a wall thickness at a midpoint of thelength of the body is less than a wall thickness at each of the firstsecond ends of the body, such that the wall thickness of the body tapersgradually from the first and second ends toward the midpoint, whereinthe body expands only in a radial direction.
 7. The bladder of claim 6,further comprising a plurality of ribs projecting from andlongitudinally along an outer surface of the bladder along a length ofthe body.
 8. The bladder of claim 6, wherein the outer diameter of thebody is constant over the length of the body.
 9. The bladder of claim 6,wherein the inner diameter of the body increases from each of the firstend and the second end toward the midpoint, wherein the body isconfigured to receive a fluid at the midpoint because the wall thicknessat the midpoint is less than the wall thickness at each of the first endand the second end such that there is less material force to overcome toinitiate filing of the bladder because of the decreased wall thickness.10. The bladder of claim 6, wherein the reduced diameter portions ofeach of the first connecting end portion and the second connecting endportion define a groove about an outer perimeter of the bladder forreceipt of an O-ring configured for securing the bladder to a mandrel.11. An elastomeric pump for an infusion assembly, comprising: aninflatable elastomeric bladder comprising: an expandable body extendinglongitudinally between opposing first and second connecting endportions, where at least a portion of an outer diameter of each of thefirst and second connecting end portions is less than an outer diameterof the body, the body extending longitudinally over a bladder lengthfrom a first bladder end adjacent the first connecting end portion to anopposing second bladder end adjacent the second connecting end portion,the body further including: a central lumen defined by an inner surfaceof the bladder, a bladder outer diameter, a bladder inner diametermeasured at the inner surface, and a wall thickness defined between thebladder outer diameter and bladder inner diameter; and a mandrelextending within the central lumen of the bladder, the mandrel defininga mandrel port in fluid communication with the central lumen of thebladder, the mandrel port disposed adjacent a midpoint of the bladderlength, wherein the bladder is disposed on the mandrel such that thebladder is sealingly secured on the mandrel at the first and secondconnecting end portions, wherein a wall thickness at the midpoint of thebladder length is less than a wall thickness at each of the firstbladder end and the second bladder end, wherein the body expands only ina radial direction.
 12. The elastomeric pump of claim 11, wherein thewall thickness at the first bladder end is greater than the wallthickness at the second bladder end.
 13. The elastomeric pump of claim11, wherein the wall thickness at the second bladder end is greater thanthe wall thickness at the first bladder end.
 14. The elastomeric pump ofclaim 11, wherein the is configured to receive a fluid from the mandrelport adjacent the midpoint of the bladder length where the wallthickness at the midpoint is less than the wall thickness at each of thefirst and second ends such that there is less material force to overcometo initiate filing because of the decreased wall thickness.
 15. Theelastomeric pump of claim 11, wherein the mandrel comprises a mandrelbody extending over a mandrel length from a first mandrel end to anopposing second mandrel end; and a mandrel outer diameter.
 16. Theelastomeric pump of claim 15, wherein the mandrel outer diameter at amidpoint of the mandrel length is greater than the mandrel outerdiameter at each of the first mandrel end and the second mandrel endsuch that the mandrel is a generally convex mandrel.
 17. The elastomericpump of claim 16, wherein the wall thickness of the bladder at themidpoint of the bladder length is less than the wall thickness at eachof the first bladder end and the second bladder end such that the wallthickness tapers from each of the first bladder end and the secondbladder end toward the midpoint of the bladder length.
 18. Theelastomeric pump of claim 11, wherein the reduced diameter portions ofeach of the first connecting end portion and the second connecting endportion define a groove about an outer perimeter of the bladder forreceipt of an O-ring that secures the bladder to the mandrel.
 19. Theelastomeric pump of claim 11, wherein the bladder further comprises aplurality of ribs projecting from and longitudinally along an outersurface of the bladder.